Add header for _Float32 testing.

This patch adds the header required for testing _Float32 function
aliases, using float ulps.  The corresponding makefile support will be
included in the main patch that enables those aliases.

In conjunction with other _Float32 changes, tested for x86_64 and with
build-many-glibcs.py.

	* math/test-float32.h: New file.

ChangeLog

@@ -1,5 +1,7 @@
 2017-12-06  Joseph Myers  <joseph@codesourcery.com>
 
+	* math/test-float32.h: New file.
+
 	* sysdeps/generic/libm-alias-float.h: Include <bits/floatn.h>.
 	[__HAVE_FLOAT32 && !__HAVE_DISTINCT_FLOAT32]
 	(libm_alias_float_other_r): Create f32 alias.

math/test-float32.h

@@ -0,0 +1,37 @@
+/* Common definitions for libm tests for _Float32.
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "test-math-floatn.h"
+
+/* Fixup builtins and constants for older compilers.  */
+#include <bits/floatn.h>
+#include <float.h>
+
+#define FUNC(function) function ## f32
+#define FLOAT _Float32
+#define CFLOAT __CFLOAT32
+#define BUILD_COMPLEX(real, imag) (CMPLXF32 ((real), (imag)))
+#define PREFIX FLT32
+#define TYPE_STR "float"
+#define ULP_IDX ULP_FLT
+#define ULP_I_IDX ULP_I_FLT
+#define LIT(x) __f32 (x)
+#define LITM(x) x ## f32
+#define FTOSTR strfromf32
+#define snan_value_MACRO SNANF32